(a) Field of the Invention
The present invention relates to a process for preparing elastic polyurethane foams and to products produced by such a process. More particularly, the invention is concerned with a process for preparing elastic polyurethane foams which involves the use of a novel polyol composition as a raw material and it is also concerned with products produced by such a process.
(B) Description of the Prior Art
It is well known to the art to produce polyurethane foams through the interaction of polyisocyanates with organic compounds having reactive hydrogen atoms in their structures. In such production, so-called "polyols" such as polyether-polyols and polyester-polyols are generally employed as said polyhydroxy compounds having a reactive hydrogen.
Polyoxypropylene glyceryl ether, polyoxypropylene diglyceryl ether, polyester of alkylene glycol and the like have hitherto been used as a polyol in the preparation of elastic polyurethane foams. However, the elastic polyurethane products produced from such polyols as mentioned above are unsatisfactory in view of their poor physical properties as in hardness, elasticity, and dimensional stability.
Under the foregoing circumstances, there has been proposed methods for preparing polyurethanes which use polyols generally referred to as "polymer-polyols" and containing a polymer of relatively high molecular weight in an attempt to eliminate the cause of the aforesaid unsatisfactory result. Such methods are disclosed, for example, in Japanese Patent Application Publication No. Sho 41-3743, the priority rights of which are claimed based on U.S. Patent Application Ser. No. 155,467 of Paul Stamberger, now abandoned but of which continuation-in-part applications have issued as U.S. Pat. Nos. 3,304,273 and 3,383,361. According to the methods of Stamberger U.S. application 155,467 (and corresponding Japanese publication No. Sho 41-3743) and Stamberger U.S. Pat. No. 3,304,273, a polymer-polyol produced by polymerizing a monomer in a polyol is employed to prepare polyurethanes. However, it is difficult for these inventions to achieve uniform polyurethane foams, because in the production of the polymer-polyol, no chemical reaction of the polymer with the polyol takes place. As to the chemical bonding status between the polymer and the polyol, Japanese Patent Application Publication No. Sho 41-3473 and U.S. application Ser. No. 155,467 only assumes the bonding formed by the graft-polymerization.
It has also been proposed to prepare a polyester-polyol by the interaction of an unsaturated dicarboxylic acid such as itaconic acid used as a part of the acid components with a polyhydroxy compound. For example, U.S. Pat. No. 2,924,581 to A. Bavley et al describes a method of preparing a polyester-polyol for use in the production of polyurethanes. According to the patent to Bavley et al, the polyester-polyol is prepared by reacting a mixture of itaconic acid and adipic acid with ethylene glycol. Since the polyester-polyol obtained by the method has a reactive double bond, it is expected that, when the polyester-polyol is used for the production of polyurethane foams, properties of the product are improved due to the simultaneous occurrence of a urethanating reaction and a radical polymerization reaction at the time of the reaction of the polyester polyol with a polyisocyanate. The radical polymerization is either the homopolymerization of the polyester-polyol per se or the copolymerization of the polyester-polyol with an added monomer having vinyl type double bonds in the presence of a polymerization catalyst. Contrary to the expectation, however in reality, the urethane foam products heretofore produced by the use of polyester-polyol have many undesirable cracks and are far from industrial use. In fact, Bavley et al add a polymerization inhibitor such as naphthoquinone after the esterification to inhibit the polymerization of the polyester-polyol and then carry out the reaction with a polyisocyanate.
Another type of polyol composition is proposed in Japanese Patent Application Publication No. Sho 49-15959 in which a polyol for use in producing polyurethane foams with improved properties is prepared by reacting an unsaturated dicarboxylic acid with an alkylene oxide. According to the method of this published application, a urethanating reaction and a radical polymerization of the polyol simultaneously take place, but an additional step is required to distill out the remaining alkylene glycol. Accordingly, the method is not free from disadvantages in its realization on an industrial scale. Furthermore, it is presumed in the method that the double bonds effective to contribute to the enhancement of properties of the polyurethane foam products are reduced in ratio. In other words, the method of the published Japanese patent application does not provide a fundamental solution of the foregoing problems encountered in the production of polyurethane foam products.
Since the known methods as described above employ a diol such as alkylene glycol or a triol of relatively low molecular weight as a polyhydroxy compound, the remaining polyol adversely affects the physical properties of the resulting products such as elasticity and hardness. Accordingly, the methods must include an additional step to remove the remaining polyol.
It is known that polyurethane foams having better properties are produced from a polyol of relatively high molecular weight than a polyol of relatively low molecular weight and that triols are much more desirable than diols for the polyol of relatively high molecular weight.